In many environmental and medical studies, it is necessary to conduct experiments involving the supply of gas or aerosol to experimental animals. Rodents such as rats, and also smaller animals, such as mice, are frequently used for this purpose. In many cases this is done through the use of relatively large chambers in which a number of animals are exposed to a common atmosphere. Such a system is shown in U.S. Pat. No. 4,216,741 to Owen R. Moss. This embodiment produces a highly uniform composition throughout the chamber.
In other cases, however, it is desired to confine the aerosol or gas to the noses alone of the animals. This may be done to reduce the amount of gaseous material used to conduct the exposure, or because it is desired for experimental purposes to restrict the dose primarily to the respiratory system of the animals. This is accomplished by so-called "nose-only exposure chambers" such as shown in U.S. Pat. No. 4,721,060 to William C. Canon, et al., and described in an article by Hsu-Chi Yeh, M. Burt Snipes, and Rick D. Brodbeck of the Inhalation Toxicology Research Institute, American Industrial Hygiene Association Journal 48(3):247-251(1987).
The '060 patent discloses a so-called "flow-past" system in which gaseous material is delivered through a small tube to the nose of each rodent. The tubes cause the flow of the gaseous material to change from vertical to horizontal thereby limiting the size of aerosol that is delivered to the nose of the animal. The Yeh et al article shows a dual-wall chimney-type design for nose-only exposure of rodents. This apparatus is designed for gaseous materials having a particle size range from 0.3 to 15.0 micrometers. Further, there is no provision for exposure of avian species.
Environmental concerns are broadening to include evaluation of avian species exposed to gaseous materials such as microbial pest control agents (MPCAs). Since the avian respiratory tract is fundamentally different from the rodent respiratory tract, the effects of gaseous material exposure of avian species cannot be accurately estimated on the basis of exposure of rodent species.
Experimental studies using birds such as described by (1) M. H. Weeks, L. A. Lawson, R.A. Angerhofer, C.D. Davenport, and N. E. Pennington, "Preliminary Assessment of the Acute Toxicity of Malathion in Animals", Arch. Environ. Contam. Toxicol., 1977, 6:23-31, (2) R. K. Myers, and L. H. Alp, "Pulmonary Clearance and Lesions of Lung and Air Sac in Passively Immunized and Unimmunized Turkeys Following Exposure to Aerosolized Escherichia Coli", Avian Diseases, 1987 31:622-628, and (3) C. S. Edison, and S. H. Kleven, "A Comparison of Various Routes of Newcastle Disease Vaccination at One Day of Age", Poultry Science, 1975, 55:1778-1787, have used whole-body exposures of free ranging birds. Whole body exposures do not provide accurate control of exposure of the respiratory tract to gaseous materials especially for gaseous materials having large (up to about 20 micrometers) particle sizes.